10,552 research outputs found
Superconductivity and Magnetism in REFeAsO1-xFx (RE=Rare Earth Elements)
Fluoride-doped iron-based oxypnictides containing rare-earth gadolinium
(GdFeAsO0.8F0.2) and co-doping with yttrium (Gd0.8Y0.2FeAsO0.8F0.2) have been
prepared via conventional solid state reaction at ambient pressure. The
non-yttrium substituted oxypnictide show superconducting transition as high as
43.9 K from temperature dependent resistance measurements with the Meissner
effect observed at a lower temperature of 40.8 K from temperature dependent
magnetization measurements. By replacing a small amount of gadolinium with
yttrium Tc was observed to be lowered by 10 K which might be caused by a change
in the electronic or magnetic structures since the crystal structure was not
altered.Comment: 4 pages, 4 figures, Journal of Physics: Conference Series
(Proceedings in the LT25 Low Temperature Physics Conference) Submitte
Investigation of passive flow control techniques to enhance the stall characteristics of a microlight aircraft
This report investigates the enhancement of aerodynamic stall characteristics of a Skyranger microlight aircraft by the use of passive flow control techniques, namely vortex generators and turbulators. Each flow control device is designed and scaled to application conditions. Force balance measurements and surface oil flow visualisation are carried out on a half-model of the microlight to further investigate the nature of the flow on the aircraft with and without the flow control devices. The results indicate a clear advantage to the use of turbulators compared with vortex generators. Turbulators increased the maximum lift coefficient by 2.8%, delayed the onset of stall by increasing the critical angle by 17.6% and reduced the drag penalty at both lower (pre-stall) and higher angles of attack by 8% compared to vortex generators. With vortex generators applied, the results indicated a delayed stall with an increase in the critical angle by 2% and a reduced drag penalty at higher angles of attack
Photon-induced production of the mirror quarks from the model at the
The photon-induced processes at the provide clean experimental
conditions due to absence of the proton remnants, which might produce
complementary and interesting results for tests of the standard model and for
searching of new physics. In the context of the littlest model with
T-parity, we consider the photon-induced production of the mirror quarks at the
. The cross sections for various production channels are calculated and a
simply phenomenology analysis is performed by assuming leptonic decays.Comment: 20 pages, 10 figure
2-DOF Lead-plus-PI Control Approach for Magnetic Levitation System
This paper proposes Two-Degree of Freedom (2-DOF) Lead-plus-PI a classical linear control system for positioning control of a magnetic levitation (maglev) system. Maglev system has practical importance in many engineering system. However, maglev has inherently nonlinear and open loop unstable characteristics. Thus, it is a challenging task to control the maglev system. In this paper, the 2-DOF Lead-plus-PI controller is developed to control the positioning performance of the maglev system as it has simple control structure and straightforward design procedure that can be designed using root locus technique and Ziegler Nichols second method. The proposed controller can be easily implemented into the maglev system without require deep knowledge in control system. The effectiveness of the proposed controller is validated experimentally. Experimental results show the 2-DOF Lead-plus-PI controller has a better positioning accuracy and transient response in point-to-point motion, as compared to Lead-plus-PI controller. The proposed controller shows a position accuracy of 40 µm, which is around the vibration amplitude of the sensor output in open loop. It also takes less than 1 second to stabilize the ball within ± 200 µm and the steady state error has improved to around 45% in point-to-point positioning performance. Besides, the proposed controller also reduced the tracking error to about 48% as compared to Lead-plus-PI controller
Mode-coupling theory for structural and conformational dynamics of polymer melts
A mode-coupling theory for dense polymeric systems is developed which
unifyingly incorporates the segmental cage effect relevant for structural
slowing down and polymer chain conformational degrees of freedom. An ideal
glass transition of polymer melts is predicted which becomes molecular-weight
independent for large molecules. The theory provides a microscopic
justification for the use of the Rouse theory in polymer melts, and the results
for Rouse-mode correlators and mean-squared displacements are in good agreement
with computer simulation results.Comment: 4 pages, 3 figures, Phys. Rev. Lett. in pres
Simultaneous computation of dynamical and equilibrium information using a weighted ensemble of trajectories
Equilibrium formally can be represented as an ensemble of uncoupled systems
undergoing unbiased dynamics in which detailed balance is maintained. Many
non-equilibrium processes can be described by suitable subsets of the
equilibrium ensemble. Here, we employ the "weighted ensemble" (WE) simulation
protocol [Huber and Kim, Biophys. J., 1996] to generate equilibrium trajectory
ensembles and extract non-equilibrium subsets for computing kinetic quantities.
States do not need to be chosen in advance. The procedure formally allows
estimation of kinetic rates between arbitrary states chosen after the
simulation, along with their equilibrium populations. We also describe a
related history-dependent matrix procedure for estimating equilibrium and
non-equilibrium observables when phase space has been divided into arbitrary
non-Markovian regions, whether in WE or ordinary simulation. In this
proof-of-principle study, these methods are successfully applied and validated
on two molecular systems: explicitly solvated methane association and the
implicitly solvated Ala4 peptide. We comment on challenges remaining in WE
calculations
A random quantum key distribution by using Bell states
We proposed a new scheme for quantum key distribution based on entanglement
swapping. By this protocol \QTR{em}{Alice} can securely share a random quantum
key with \QTR{em}{Bob}, without transporting any particle.Comment: Accepted by J. Opt. B: Quantum Semiclass. Op
Imaging Orbital-selective Quasiparticles in the Hund's Metal State of FeSe
Strong electronic correlations, emerging from the parent Mott insulator
phase, are key to copper-based high temperature superconductivity (HTS). By
contrast, the parent phase of iron-based HTS is never a correlated insulator.
But this distinction may be deceptive because Fe has five active d-orbitals
while Cu has only one. In theory, such orbital multiplicity can generate a
Hund's Metal state, in which alignment of the Fe spins suppresses inter-orbital
fluctuations producing orbitally selective strong correlations. The spectral
weights of quasiparticles associated with different Fe orbitals m should
then be radically different. Here we use quasiparticle scattering interference
resolved by orbital content to explore these predictions in FeSe. Signatures of
strong, orbitally selective differences of quasiparticle appear on all
detectable bands over a wide energy range. Further, the quasiparticle
interference amplitudes reveal that , consistent with
earlier orbital-selective Cooper pairing studies. Thus, orbital-selective
strong correlations dominate the parent state of iron-based HTS in FeSe.Comment: for movie M1, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M1.mp4, for movie M2, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M2.mp4, for movie M3, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M3.mp4, for movie M4, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M4.mp4, for movie M5, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M5.mp
- …